A braking pressure control unit is applied to a vehicle braking system, which generally has a function for an anti-lock braking control (ABS), a function for a vehicle stability control (ESC), and so on. The braking pressure control unit is composed of a combination of a hydraulic pressure control block in which a pump and electromagnetic valves are assembled in a housing thereof, an electric motor for driving the pump, and an electronic control unit having a motor driving circuit and a valve control circuit. A valve which controls the brake fluid pressure in the respective wheel cylinders can be used as the above electromagnetic valve. A pressure sensor and other electrical parts may be also assembled to the braking pressure control unit, as the case may be. A braking pressure control unit of this kind is disclosed, for example, in Japanese Patent Publication No. H10-129445 or No. H11-165626.
In the braking pressure control unit disclosed in the above Japanese Patent Publication No. H10-129445 or No. H11-165626, each of two systems for the brake fluid circuits has two pumps, which are driven by one electric motor. The electric motor and an electronic control unit are arranged in a direction of a motor shaft. In the braking pressure control unit disclosed in the above Japanese Patent Publication No. H10-129445, an electronic control unit is integrally formed with an electric motor, wherein a printed circuit board is fixed to a part of the electric motor. In the braking pressure control unit disclosed in the above Japanese Patent Publication No. H11-165626, an electric motor for driving a pump and electromagnetic valves (coil portions thereof) are arranged at one side of a housing for a hydraulic pressure control block, in such a manner that the electric motor and the electromagnetic valves are not overlapped with each other. The type of the electric motor is not explained in the above Japanese Patent Publication No. H11-165626.
Another Japanese Patent Publication No. H10-203338 discloses a vehicle braking system of a brake-by-wire type, in which a plurality of pumps (generally, four pumps) are provided for each of wheel cylinders, those pumps are divided and arranged for the two systems of brake fluid circuits, and those pumps are driven by two electric motors.
The braking pressure control unit is generally mounted in an engine compartment of a vehicle. Therefore, when a size of the braking pressure control unit becomes larger, it may cause a problem that the braking pressure control unit will not be easily mounted in the engine compartment due to a lack of a space therefor. It is, therefore, important to make the size of the braking pressure control unit as smaller as possible. In the above explained braking pressure control unit (Japanese Patent Publication No. H10-129445 or No. H11-165626), in which the electric motor and the electronic control unit are arranged in the direction of the motor shaft, a longitudinal length of the braking pressure control unit becomes inevitably longer and may be affected by space limitations for the engine compartment.
In a structure, in which the electric motor and the electronic control unit are integrally provided it may become a problem that electrical or electronic parts included in the electronic control unit are deteriorated due to heat generated at the electric motor.
In the conventional braking system, as disclosed in the above Japanese Patent Publication No. H10-203338, numbers of the electric motors and pumps are increased compared with the other braking systems, the size of the braking pressure control unit becomes inevitably larger and it is more likely to be affected by the space limitations for the engine compartment.
It is proposed to use a brushless motor for the braking pressure control unit, in place of a brush-type motor for driving the pump. Since the brushless motor is superior to the brush-type motor in its response, a pressure increasing speed is increased and a response for braking operation can be improved, when the brushless motor is used. However, the brushless motor requires electrical parts, such as a condenser and a coil, which are necessary for a noise filter and generally large in size. When the electronic control unit, in which such electrical parts having large sizes are included, is arranged at one side of the electric motor in the motor shaft direction, the length of the braking pressure control unit becomes further longer. And such braking pressure control unit is easily affected by the space limitations for the engine compartment.
The problem of the deterioration for the electronic parts due to the heat generated by the electric motor may be solved by the electric motor and the electronic control unit, which are separately formed from each other and arranged at both sides of the braking pressure control unit. In such a structure, however, the electric connection between the electric motor and the electronic control unit become very complicated. In addition, it causes a problem that the size of the braking pressure control unit becomes much larger due to the complicated wiring arrangement.
The brushless motor generally has three lines for electric power supply and five lines for control signals. In the case that two brushless motors are used, a total of sixteen wires should be formed from a wire harness, for which countermeasure for noise suppression is necessary. When the electric (brushless) motors and the electronic control unit are arranged at opposite sides of the braking pressure control unit, they are connected by the above wire harness. Accordingly, the increase of the size of the braking pressure control unit, which is also caused by the increase of the wire harness, becomes much larger.